What is the standard of review in a civil case where a judge has found that a plaintiff has been ordered to proceed pursuant to an invalid regulation?

The standard of review is set forth in section 1094.5, subdivision (b) of the Code of Civil Procedure: "The inquiry in such a case shall extend to the questions whether the respondent has proceeded without, or in excess of, jurisdiction; whether there was a fair trial; and whether there was any prejudicial abuse of discretion. Abuse of discretion is established if the respondent has not proceeded in the manner required by law, the order or decision is not supported by the findings, or the findings are not supported by the evidence." " 'Proceeding pursuant to an invalid regulation is not proceeding in the manner required by law." (Woods, supra, 28 Cal.3d at p. 678.) We review questions of law de novo. (Antelope Valley Press v. Poizner (2008) 162 Cal.App.4th 839, 851.)